ECHINOCYAMUS PUSILLUS. 



I. 



Methods. 



Considering how difficult it is to bring the larvée of Echinoids 

 from artificially fertilized eggs into conditions older than the Pluteus 

 stage, as may be understood from the numerous experiments of other 

 investigators, who have never succeeded in bringing them to full ma- 

 turity, I think it may be useful to explain somewhat fully the methods 

 by means of which I managed to get larvae developed in the aquaria 

 through all the different stages of metamorphosis from the egg to the 

 young sea-urchin. 



During my first summer stay at the Swedish biological marine 

 station I never succeeded in bringing larvge of Echinocyamus to any 

 advanced stage of development. The oldest larvae I obtained in the 

 aquaria that summer were Plutei, but, as they were mostly in want of the 

 final pair of arms and calcareous spicules, even these had not reached 

 a stage of full Pluteus maturity. In consequence of this no other choice 

 was left me than to attempt to collect the older stages by means of 

 Müller's tow-net from the surface of the sea. During the breeding- 

 experiments I usually kept the larvge in tanks of glass of a capacity of 

 4 to 5 liters and containing either sea-water alone or sea-water with some 

 green marine plants; in the former case the larvae were almost -devoid 

 of pigment, and in both cases they did not live beyond six weeks. I 

 also placed basins and cylinders of glass in ice, in order to imitate the 

 coolness at the bottom of the sea, but even these experiments were 

 without result; the development of the larvae was only delayed, so that- 

 the Blastula stage for instance, which at an ordinary room temperature 

 is reached during the course of the first day, in this case was not arrived 

 at till after two or three days. 



Finally I took large glass cylinders of a capacity of 15 or 20 

 liters, in which were placed a great number of larvae and fertilized eggs, 

 and let them drift about on the surface of the sea in an almost vertical 

 position with the wide opening very carefully closed with an extremely 

 fine-meshed canvas. By the movement of the sea currents and change 

 of water were efi'ected, but this experiment was also unsuccessful. 



On account of the great importance for a successful study of the 

 embryology of Echinoderms and other invertebrates of obtaining complete 





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